A conventional semi-closed rebreathing scuba system is illustrated in FIG. 1 labeled "PRIOR ART". This prior art system 10 includes a supply circuit 12 and a breathing circuit 14. The supply circuit 12 which supplies fresh breathable gas (not yet inhaled) to the breathing circuit 14 includes a pressurized tank 16, a regulator 18 and a flow control device 20. The breathing circuit 14 includes an expandable respiration bellows 22 connected to an inhalation conduit 24 which, in turn, is connected to a mouthpiece assembly 26. An outlet portion of the mouthpiece assembly 26 is connected to an exhalation conduit 28 which reconnects to the respiration bellows 22 through a carbon dioxide absorber 30. The respiration bellows 22 also includes an outlet valve 32 allowing a controlled amount of gas to exit the system (hence the term, semi-closed).
In operation of this prior art rebreathing system, the pressurized air from the supply circuit 12 is introduced into the breathing circuit 14 at the respiration bellows 22. The fresh supply-gas is mixed in the respiration bellows 22 with the exhaled gas that has passed from the diver (not shown) through the outlet side of the mouthpiece assembly 26, the exhalation conduit 28, the carbon dioxide absorber 30 and into the respiration bellows 22. As the diver inhales, the mixed gas from the bellows 22 is forced through the inhalation conduit 24 and the inlet portion of the mouthpiece assembly 26. The mouthpiece assembly 26 includes one-way check valves to prevent the direct rebreathing of any exhaled gas and to otherwise ensure the proper transfer of gases between the diver and the rebreathing equipment. As this breathing cycle is repeated around the breathing circuit 14 of the breathing system 10, waste gases, including carbon dioxide, expired by the diver, are removed from the breathing circuit 14 by the carbon dioxide absorber 30. Waste gas that is removed from the breathing circuit 14 is replaced with a supply of fresh gas from the supply circuit 12. The regulator 18, the flow control device 20, the expandable respiration bellows 22 and the outlet valve 32 work together to ensure that the pressure of the gas within the breathing circuit 14 remains at a constant and safe level regardless of the surrounding environment.
One problem with the above-described prior art semi-closed scuba breathing system relates to the handling of moisture introduced into the breathing circuit 14. Water may enter the breathing circuit 14 in the form of water vapor carried by the exhaled gases of the diver or through a leak in the system from the outside environment. In either case, water has a detrimental effect on the carbon dioxide absorber, effectively reducing the ability of the absorber to remove waste gas from the breathing circuit 14. Any water entering the exhalation conduit 28 of the prior art system of FIG. 1 will pass directly into the carbon dioxide absorber 30, and prematurely render the absorber 30 ineffective. Additionally, water entering the breathing circuit 14 will eventually accumulate in the respiration bellows 22. Depending on the orientation of the diver, the accumulated water in the respiration bellows 22 may easily enter the inhalation conduit 24 of the breathing circuit 14 and endanger the safety of the diver.
It is an object of the invention to provide a semi-closed rebreathing apparatus which overcomes the above-mentioned problems.
It is another object of the invention to provide a semi-closed rebreathing apparatus which automatically removes any water accumulated within the system.
It is yet another object to increase the time span during which a carbon dioxide absorber within a rebreathing system will remain effect.
It is still another object to provide an improved semi-closed rebreathing system for firefighting and other environments.